The present invention relates to a method of and apparatus for generating a tone waveform by a computer executing a software program to calculate tone waveform sample values, to thereby allow a CPU or processor of a micro computer system to function as a tone generator.
Electronic musical instruments are conventionally known which implement a tone generator circuit by a tone generating software program executed by a CPU. In order to reproduce a tone waveform with such known electronic musical instruments, it is necessary to supply tone waveform sample values to a digital-to-analog converter (DAC) regularly in response to clock pulses corresponding to a predetermined sampling frequency. The conventionally-known electronic musical instruments are designed to generate tone waveform samples by performing tone Generating calculation in response to Generation of each clock pulse. But, calculating a tone waveform sample value in response to each such clock pulse would undesirably result in inefficient operation of the CPU because preparing for and ending each tone waveform sample value calculation require a considerable overhead.
To provide a solution to the problem, it has been proposed to calculate a plurality of tone waveform sample values together for each relatively long, optional calculating clock pulse that is generated once every predetermined plurality of sampling clock pulses. However, in cases where the tone generating software program is run concurrently with other software, such as business or game software, burdens on the CPU tend to be significantly great because tone waveform sample values for a plurality of samples have to be calculated in response to each calculating clock pulse, thus resulting in operational delays of the other software.